A protein array (protein chip) is a technology providing new possibilities as a means for investigating functions of unknown proteins encoded by genes or analyzing complicated interactions among a large number of proteins at once. The protein array is provided by aligning a protein or a peptide on a substrate, and various protein arrays have been reported (see Patent Documents 1 and 2). In protein array technology, a protein is immobilized on an appropriate substrate, the immobilized protein is brought into interaction with another protein or the like, and the interacting spots on the array are detected.
The detection of spots on an array is carried out by using a compound labeled with a fluorescent dye or the like and capable of interacting with the immobilized protein and measuring the fluorescence emission from the fluorescent dye on the array. This method, however, requires preparing a label preparation and has the problem that the activity of a protein may be decreased by labeling of the protein. In addition, equipment for measuring an array using a fluorescence-measuring device or the like is not widely used. Further, the interaction between proteins cannot be analyzed in real time.
In order to solve these problems, a detection process by surface plasmon resonance (SPR) imaging has been developed (see Non-Patent Documents 1 and 2). In this process, a protein immobilized on a protein array is detected by irradiating the array with a polarized beam to give an SPR image of the reflected light and analyzing the reflection light intensity of the SPR image. This process has advantages that a label is not required and that the detection can be performed in real time. However, the interaction between an immobilized protein and a low-molecular substance cannot be analyzed even if the SPR imaging process is employed, and also this process has the problem that the dynamic range is narrow. In addition, there are problems that equipment used for SPR imaging is extremely expensive and that construction of a detection system is not easy.
Further, though a detection process using a protein array having a crystal oscillator integrated thereinto has been reported (see Non-Patent Document 3), this process has the same problems as in the above-described SPR imaging process.
In addition, though a detection process utilizing microscopic Fourier transform infrared spectroscopy (micro FT-IR) has been reported (see Patent Document 3), the measurement apparatus is expensive, and the process is not necessarily suitable for quantitative determination.
[Patent Document 1] JP Patent Publication (Kohyo) No. 2002-520618A
[Patent Document 2] JP Patent Publication (Kohyo) No. 2002-502038A
[Patent Document 3] JP Patent Publication (Kokai) No. 2004-45390A
[Non-Patent Document 1] Nelson, B. P., et al., Anal. Chem., 71(18), 3928-3934 (1999)
[Non-Patent Document 2] Brockman, J. M., et al., Annu. Rev. Phys. Chem., 51, 41-63 (2000)
[Non-Patent Document 3] Y. Okahata, et al., J. Am. Chem. Soc., 114, 8299-8300 (1992)